攔截asp.net輸出流做處理

本文標題是指對已經生成了HTML的頁面做一些輸出到客戶端之前的處理。

方法的原理是：把Response的輸出重定向到自定義的容器內，也就是我們的StringBuilder對象里，在HTML所有的向頁面輸出都變成了向StringBuilder輸出，然后我們對StringBuilder處理完成之后，再把Response的輸出重定向到原來的頁面上，然后再通過Response.Write方法把StringBuilder的內容輸出到頁面上

這里之所以用反射，是因為Response對象的OutPut屬性是只讀的，通過反編譯該類的程序集發現，OutPut實際上是內部私有成員 _writer來實現輸出的。因此通過反射來改寫該成員的值以實現輸出流的重定向。

1. usingSystem;
2. usingSystem.Collections.Generic;
3. usingSystem.Linq;
4. usingSystem.Web;
5. usingSystem.Web.UI;
6. usingSystem.Web.UI.WebControls;
7. usingSystem.Text;
8. usingSystem.IO;
9. usingSystem.Reflection;
11. publicpartialclass_Default:System.Web.UI.Page
12. {
13. StringBuildercontent=newStringBuilder();
14. TextWritertw_old,tw_new;
15. FieldInfotw_field;
17. PRotectedvoidPage_Load(objectsender,EventArgse)
18. {
19. varcontext=HttpContext.Current;
21. tw_old=context.Response.Output;//Response原來的OutPut
22. tw_new=newStringWriter(content);//一個StringWriter,用來獲取頁面內容
23. vartype_rp=context.Response.GetType();
24. //通過反射獲取對象的私有字段
25. tw_field=type_rp.GetField("_writer",System.Reflection.BindingFlags.Public|System.Reflection.BindingFlags.NonPublic|System.Reflection.BindingFlags.Instance);
26. tw_field.SetValue(context.Response,tw_new);
27. }
29. protectedoverridevoidRender(HtmlTextWriterwriter)
30. {
31. base.Render(writer);
32. //替換回Response的OutPut
33. tw_field.SetValue(HttpContext.Current.Response,tw_old);
34. //做自己的處理
35. content.AppendLine("<!--江湖小子-->");
36. HttpContext.Current.Response.Write(content.ToString());
37. }
38. }
40. 方法二，用HttpModul來實現：
42. usingSystem;
43. usingSystem.Collections.Generic;
44. usingSystem.Linq;
45. usingSystem.Web;
46. usingSystem.Web.UI;
47. usingSystem.IO;
48. usingSystem.Text;
49. usingSystem.Reflection;
51. ///<summary>
52. ///HttpModule的摘要說明
53. ///</summary>
54. publicclassHttpModule:IHttpModule
55. {
56. privateHttpapplication_contextApplication;
57. privateTextWritertw_new,tw_old;
58. privateStringBuilder_content;
59. privateFieldInfotw_field;
61. publicvoidInit(HttpApplicationcontext)
62. {
63. _contextApplication=context;
64. _contextApplication.PreRequestHandlerExecute+=newEventHandler(_contextApplication_PreRequestHandlerExecute);
65. }
67. publicvoidDispose()
68. {
69. _contextApplication=null;
70. _contextApplication.Dispose();
71. }
73. publicvoid_contextApplication_PreRequestHandlerExecute(objectsender,EventArgse)
74. {
75. HttpContextcontext=_contextApplication.Context;
77. var_page=context.HandlerasSystem.Web.UI.Page;
78. _page.Unload+=newEventHandler(_page_Unload);
80. _content=newStringBuilder();
81. tw_old=context.Response.Output;//Response原來的OutPut
82. tw_new=newStringWriter(_content);//一個StringWriter,用來獲取頁面內容
83. vartype_rp=context.Response.GetType();
84. tw_field=type_rp.GetField("_writer",System.Reflection.BindingFlags.Public|System.Reflection.BindingFlags.NonPublic|System.Reflection.BindingFlags.Instance);
85. tw_field.SetValue(context.Response,tw_new);
86. }
89. void_page_Unload(objectsender,EventArgse)
90. {
91. //替換回Response的OutPut
92. tw_field.SetValue(HttpContext.Current.Response,tw_old);
93. //做自己的處理
94. _content.AppendLine("<!--江湖小子-->");
95. HttpContext.Current.Response.Write(_content.ToString());
96. }
98. }
100. 方法三：
101. publicclassHttpModule:IHttpModule
102. {
103. privateHttpApplication_contextApplication;
104. privateTextWritertw_new,tw_old;
105. privateStringBuilder_content;
106. privateFieldInfotw_field;
108. publicvoidInit(HttpApplicationapplication)
109. {
110. _contextApplication=application;
111. _contextApplication.BeginRequest+=newEventHandler(_contextApplication_BeginRequest);
112. _contextApplication.EndRequest+=newEventHandler(_contextApplication_EndRequest);
113. }
115. void_contextApplication_BeginRequest(objectsender,EventArgse)
116. {
117. _content=newStringBuilder();
118. tw_old=_contextApplication.Response.Output;
119. tw_new=newStringWriter(_content);
120. vartype_rp=_contextApplication.Response.GetType();
121. tw_field=type_rp.GetField("_writer",System.Reflection.BindingFlags.Public|System.Reflection.BindingFlags.NonPublic|System.Reflection.BindingFlags.Instance);
122. tw_field.SetValue(_contextApplication.Response,tw_new);
123. }
125. void_contextApplication_EndRequest(objectsender,EventArgse)
126. {
127. tw_field.SetValue(_contextApplication.Response,tw_old);
128. //做自己的處理
129. _content.AppendLine("<!--jhxz-->");
130. _contextApplication.Response.Write(_content.ToString());
131. }
133. publicvoidDispose()
134. {
135. _contextApplication=null;
136. _contextApplication.Dispose();
137. }
138. }

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